Sheet feed method, a sheet feeder, and an image forming apparatus incorporating the sheet feeder

ABSTRACT

A method for use in a sheet feeder having a sheet stacking unit with a bottom plate to support a sheet bundle in which air is blown against a side edge of the sheet bundle near the topmost sheets of the bundle, thereby lifting these sheets from the bundle, and separating the uppermost sheet from the bundle, and conveying this sheet away from the bundle, wherein the lifting of the sheets when the bundle is nearly depleted is assisted by forcing an element situated underneath the bundle to push against the bundle solely when air is blown against the side edge of the bundle. A sheet feeder suitable for applying the present method and an imaging apparatus for incorporating the sheet feeder is also provided.

This application claims the priority benefits of European PatentApplication No. 05108187.5 filed on Sep. 7, 2005 which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

The present invention pertains to a sheet feed method for use in a sheetfeeder having a sheet stacking unit provided with a bottom plate tosupport a sheet bundle whenever air is blown against a side edge of thesheet bundle near the topmost sheets of the bundle, thereby liftingthese sheets from the bundle, separating the uppermost sheet from thebundle, and conveying this sheet away from the bundle. The presentinvention also pertains a sheet feeder and an imaging apparatusincorporating the sheet feeder.

A sheet feed method is known from US patent application 2004/0089994 A1.This method has been devised in order to be able and reliably feed avery broad range of recording media from the same sheet stacking unit.Nowadays, in printing rooms there are growing requests to form images oncardboard, tracing paper, and all sorts of coated media, etc. Many ofsuch media have very smooth surfaces and with sheet feeding methodsbased on friction, mis-feeds and double-feeds occasionally occur. Inorder to mitigate these problems, known methods handle the sheet feedingby first blowing air from a side edge of a paper bundle, causing of theuppermost sheets to left off of the bundle. Then, air is injectedbetween the uppermost and adjacent sheet, providing a very reliableseparation of the uppermost sheet from the bundle. The actual separationis effected by using a suction unit, followed by conveying the sheet ona conveying belt. Over the friction based methods, the air separationmethods has the advantage of a wide latitude of paper feed settingconditions, combined with the adaptability for high-speed processing,high durability and corresponding low running costs.

The known method however has an important disadvantage. It appears thatthe reliability of the feeding process decreases significantly when thebundle is nearly depleted, i.e., when less than 25 sheets of receivingmedia are present, particularly when less than 10 sheets are present.This is not restricted to extraordinary heavy or light media types. Forexample, with all sorts of plain paper, when less than 5 sheets arepresent, a mis-feed occasionally occurs. For the lighter types,typically types of less than 100 grams/square meter, the risk ofinducing skew increases significantly when less than 5 to 10 sheets arepresent. Heavier types of media seem to be prone to mis-feeds, inparticular when narrow paper formats (SEF) are being used. In order toovercome this problem, it is proposed to leave the last few sheets,typically 25-50 sheets, in the tray and than denote the tray as “empty”.These left-over sheets however, have to be removed from time to time, orimmediately when another media type is going to be loaded in the sheetstacking unit. This prior art solution therefore is far from ideal.

SUMMARY OF THE INVENTION

The present invention has as an object to overcome or at least mitigatethe above-mentioned problems. To this end a method is provided forassisting the lifting of the sheets when the bundle is nearly depletedby forcing an element situated underneath the bundle to push against thebundle, solely when air is blown against the side edge of the bundle. Inthis method, when the bundle is nearly depleted there is induced anextra force to lift the last few sheets in the direction of theseparation unit. Contrary to what one expects, it appears that when onlya few sheets are present in the tray, extra help is needed to induce anadequate lift of the sheets in the direction of the separation unit. Itis further recognized that this extra help should only be used inconnection with the blowing action against the side edge of the bundle.Thus, when the blowing action stops in order to let the remaining sheetsfall back to the bottom plate, the element should cease its liftingaction. Therefore, the present invention is clearly distinct from theprior art feed methods which make use of bottom elements that constantlyforce a bundle of sheets upwardly in the direction of a separation unit,for example because part of the bottom is forced upwardly with a spring.

In one embodiment, the blowing of the air creates a pressure differencethat forces the element to undertake an upward movement. In thisembodiment the mere air blowing action causes the element directly tomove in an upward direction. This has the advantage that there is noneed for an extra process, next to the air blowing, to provide theelement creating the needed lifting force. Next to this, because in thisembodiment the element moves upwardly as a direct result of the airblowing process, the prerequisite of an extra force being present onlyin concurrence with the air blowing action is automatically fulfilled.

In another embodiment, the element is hinged in the bottom plate. Inthis embodiment the element is connected to the bottom plate at one endbut is able to move upwardly because the connection allows a hingingaction of the element. This appears to markedly increase the reliabilityof the present feeding method, most probably because the element willalways come back to its original position when the air blowing actionstops.

The present invention also pertains to the feeder itself. With respectto the above-identified prior art, in the feeder comprises an elementthat is operatively connected to the stacking unit, the element beingconstituted such that it undertakes an upward movement solely when airis blown against the side edge of the bundle when it is nearly depleted.The working action of the element has been addressed alreadyhereinabove.

In another embodiment, the element is sheet-like. This has the advantagethat the element does not take up too much space, and also, that it caneasily be situated between the bottom plate and the sheet bundle. Inthis way, the element will hardly interfere with the process of fillingthe stacking unit with a new bundle of sheets.

In a further embodiment the element is a rigid plate that covers a partof the bottom plate. In this embodiment, the element is constituted as arigid plate in contrast with an element that is constituted as aflexible sheet. This decreases the risk of the element getting damagedby the multiple actions of stacking new bundles of sheets in thestacking unit. A rigid plate is less prone to damaging, such as inducingwrinkles, folds etc., as in a sheet-like element.

In yet a further embodiment, the rigid plate is situated essentiallyadjacent the air blowing means. Surprisingly it appears that it issufficient for the rigid plate to extend only in the direct vicinity ofthe air blowing means. Thus, there is no need for a large rigid platethat extends substantially over the complete side edge of the bundle ofsheets. This makes the construction of the stacking unit more simple.

As a further improvement, the bottom plate can be provided with a recessin which the rigid plate is situated. In this way, the rigid plate doesnot constitute an obstruction for the lowermost sheets of a new bundlethat is being loaded in the stacking unit. The recess can be made justas deep as the rigid plate is thick such that, in essence, the bottom ofthe stacking unit remains evenly flat. In this way, there is hardly anychance that sheets get damaged because of the presence of the rigidplate.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will now be exemplified in greater detail by thefollowing figures and accompanying description, wherein.

FIG. 1 is a sectional view illustrating an imaging apparatus;

FIG. 2 is a perspective view representing a sheet stacking and feedingunit;

FIGS. 3A to 3C, illustrate the lifting and separation action whenfeeding a single sheet; and

FIG. 4 shows a part of the bottom plate of the sheet stacking unitaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 represents an imaging device as is known from US 2004/0089994 A1and described elaborately in the paragraphs [0024] to [0034] of this USpatent application which paragraphs are incorporated herein bereference. This apparatus includes an image reader 200, a printer 300and a paper feed section 400. This section has paper decks 401 and 451that share a paper feeding mechanism.

The image reader is equipped with a so called ADF 100. This ADFautomatically feeds original documents to the image reader 200, inparticular from tray 101 to glass platen 102. Thereafter, it dischargesthe sheets to paper discharge tray 112. When the original passes platen102 it is read by scanner unit 104. This unit comprises lamp 103, thelight of which is reflected via the original to lens 108 and furtherthrough mirrors 105, 106 and 107. Ultimately, the light forms an imageon image sensor 109. This sensor converts the optical image into imagedata which data are outputted from the sensor and subjected to apredetermined processing in an image signal control unit (not shown).Then, the image data are inputted as video signals to an exposurecontrol section 110 of printer 300. The exposure control section 110modulates laser light and outputs this light on the photosensitive drum111. The electrostatic latent image on the drum 111 is visualised byapplication of a developer supplied by a developing device (not shown).A resist roller 115 conveys the sheet fed by the paper decks 401 and451, between the drum 111 and a transfer section 116 in a timed relationwith the laser light. The sheet on which the developer image has beentransferred is conveyed to fixing section 117 and then discharged totray 119 by a first discharge roller 118, or discharged to tray 121 bythe second discharge roller 120.

Next, the air sheet feeding and stacking units, i.e., the paper decks401 and 451 will be described. Here, the paper decks 401 and 451 areonly different in the maximum number of storage sheets, and hence, thesame reference numbers are used to denote the same or equivalentcomponents. The following description is based on paper deck 401.

FIG. 2 is a perspective view of the air sheet-feeding paper deck 401.The paper deck is arranged to stack and store a sheet bundle S on abottom plate 403. This bottom plate is provided in a repository 402 andis movable up and down. At the respective lower edges on the oppositesides of the repository 402, there are provided rails 404 and 405, whichcan be drawn to the front side with respect to the imaging apparatusbody (i.e., to the operator side of the apparatus). The front end andrear end of the bundle S are fixedly placed in predetermined positionsby plates 406 and 412. The opposite side edges are respectively placedin predetermined positions by side regulating plates 410 and 411.

At a position above the sheet bundle S, there is provided a sheet feedsection 409 serving as a sheet suction and conveying means for theuppermost sheet of the bundle. The sheet feed section 409 has a suctionduct 408 connected to a suction generating unit (not shown) forgenerating a suction pressure above the sheet bundle. A suction belt407, capable of paper feed rotation in the paper feed direction, isprovided with a large number of holes and surrounds the suction duct408. The sheet feed section 409 feeds a sheet by causing the uppermostsheet to adhere to the suction belt 407 and rotating the belt in thepaper feed direction.

In FIGS. 3A to 3C the construction and operation of the air blowingmeans and separation action of the present invention will be outlined ingreater detail. FIGS. 3A to 3C are sectional views when FIG. 2 is seenfrom the paper feed direction. Here the side regulating plate 410 hastherein a structure which serves as the air blowing means. This airblowing means includes a blowing fan 417 (see FIG. 2) serving as thesupply source of blown air, and a blowing duct 413 having at one endthereof an opening 414 (see also FIG. 2) that is opened facing the sideedge of the sheet bundle S stacked in the repository 402. There is alsoprovided an air knife 415 which has a very thin elongated opening forblowing air against the front end side of the sheet bundle S, inparticular between the two uppermost sheets.

The operations of the sheet feed system are now described here below.When a sheet bundle is set in deck 401, the bottom plate 403 is lift upto a predetermined height by using sheet height detection means (notshown) and a lift-up motor (not shown). In this embodiment, pressing astart button of the imaging apparatus starts the paper feedingoperation.

As illustrated in FIG. 3B, first the air blowing means 413 starts toblow air against the side edge of bundle S. This creates a lift-upaction for the uppermost 5 to 7 sheets (in this particular embodiment).Then, the suction generating unit located at the upper position starts asuction operation, and the suction duct 408 starts the suction action.At the same time air is blown through air knife 415 and injected betweenthe uppermost sheet and the second sheet. This also forces the uppermostsheet to be lifted somewhat more in the direction of suction unit 409.This leads to sheet 416 being attracted to the suction belt 407. Then,the air knife and air blowing means stop their blowing action so thatthe sheets that have been lifted off fall back in the direction of thebottom plate (see FIG. 3C). By drive-rotating the suction belt 407 atthis point of time, sheet 416 is delivered. Repeating this operationallows sheets to be separately and reliably fed one by one. In order toalso provide the same reliability when the bundle S is nearly depleted,for example when less than 10 sheets are present, there is provided foran extra means to assist in the lifting action caused by the air blowingmeans 413. The, the means provided for creating this extra liftingaction is outlined in greater herein below.

FIGS. 4A and 4B show a part of the bottom plate 403 of the sheetstacking unit according to the present invention. In this embodimentplate 403 is provided with a recess 421 adjacent opening 414 in sideregulating plate 410. In the recess there is provided for a rigid plate420, such that the upper surface of the rigid plate coincides with theupper surface of the bottom plate 403. Rigid plate 420 is connected tothe bottom plate 403 via hinges 422 and 423. This enables the rigidplate to undertake a predetermined upward movement as is shown in FIG.4B. This figure shows the upward movement of rigid plate 420 when theair blowing means blows air through opening 414 in the direction ofbottom plate 403. It appears that the upward action of the rigid platemarkedly improves the reliability of the sheet separation y. The reasonfor this might be that the rigid plate somehow resembles the liftingaction that is also induced when a sufficient amount of sheets arepresent (i.e., when the sheet bundle is not nearly depleted). Note thatthe upward action of the rigid plate will only be undertaken when thebundle is nearly depleted. It is only when the bottom plate has beenlifted far enough to reach the opening 414 that the rigid plate can beforced to undertake an upward movement due to the pressure differencecaused by the air blowing means. Lastly it is noted that the rigid platecan also be part of a small overlay plate, e.g. a plate such as that ofUS design patent 249,695.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A method of dispensing sheets from a sheet bundle which comprises:blowing air against a side edge of the sheet bundle near the topmostsheets of the bundle, thereby lifting these sheets from the bundle,separating the uppermost sheet from the bundle, and conveying this sheetaway from the bundle; wherein when the bundle is nearly depleted, thelifting of the sheets from the bundle is assisted by forcing an elementsituated underneath the bundle to push against the bundle solely whenair is blown against the side edge of the bundle.
 2. The methodaccording to claim 1, wherein the blowing of the air creates a pressuredifference that forces the element to undertake an upward movement. 3.The method according to claim 1, wherein the element pushes against thebundle in a hinging action.
 4. A sheet dispensing device whichcomprises: a sheet stacking unit with a bottom plate for supporting asheet bundle, air blowing means for blowing air against a side edge ofthe sheet bundle, and sheet conveying means) for conveying sheets one byone from the bundle, the conveyance being of an uppermost sheet of thebundle; wherein the dispensing device comprises an element that isoperatively connected to the stacking unit, said element beingconstructed such that it is adapted to undertake an upward movementthereby lifting the bundle solely when air is blown against the sideedge of the bundle and solely when the bundle is nearly depleted.
 5. Thesheet dispensing device of claim 4, wherein the element is sheet like.6. The sheet dispensing device of claim 5, wherein the element is arigid plate that covers a part of the bottom plate.
 7. The sheetdispensing device of claim 6, wherein the rigid plate is situatedessentially adjacent the air blowing means.
 8. The sheet dispensingdevice of claim 7, wherein the bottom plate has a recess in which therigid plate is situated.
 9. The sheet feeder of claim 4, wherein theelement is hinged to the bottom plate.
 10. An imaging apparatuscontaining the sheet dispensing device of claim 4.